The purpose of this project is to determine whether DNA sequence differences in the promoter regions of the several human globin genes are relevant to their developmental regulation. In the past, our studies have focused on the gamma globin gene promoter. In experiments that utilize recombinant DNA vectors in which the gamma globin gene promoter is linked to the coding sequences for neomycin resistance marker, we have shown that 385 bp of sequence are sufficient for erythroid specific expression as tested by stable transformation of various cell lines. Linker scanning mutants in which a synthetic linker replaces portions of the promoter have been constructed so as to delete and/or replace conserved sequences within the promoter region. Studies utilizing these mutant promoters have shown that the duplicated "CCAAT" segment, the feature by which the gamma promoter differs from that of the beta globin gene, is not required for promoter function in either erythroid or non-erythroid cells. Hybrid promoters containing portions of the gamma and beta promoter regions are being constructed in an effort to define those sequences that determine developmentally specific regulation of the gamma globin gene. These experiments utilize the human erythroleukemia cell line, K562, in which the gamma globin gene but not the beta globin gene is expressed.